Catalin_a wrote:Thank you for reply, but how can I add the additive inverse of a to both sides when a is only on one side.

Can some one please solve this, I will have more sense if I can see it solved.

Please excuse my english, I am not an english speaker.

Surely, a is on one side but not the other. The number a and its additive inverse are different numbers. You want to add THE ADDITIVE INVERSE of a to BOTH SIDES of the equation so that you can eliminate a from one side and to maintain equality.

Essentially you want to subtract a from both sides. The idea is that a + -a = 0